feat(auditlog): site script-side emitters stamp ExecutionId

Move the per-script-execution Guid on ScriptRuntimeContext from
_auditCorrelationId to _executionId, and stamp it into the dedicated
AuditEvent.ExecutionId column on every script-side audit row:

- Sync ApiCall / DbWrite: ExecutionId set; CorrelationId reverts to
  null (a sync one-shot call has no operation lifecycle).
- Cached-call script-side rows (CachedSubmit, immediate-completion
  ApiCallCached + CachedResolve) and NotifySend: ExecutionId set;
  CorrelationId unchanged (per-operation TrackedOperationId /
  NotificationId).

Renames the threaded ctor param/field across ExternalSystemHelper,
DatabaseHelper, AuditingDbConnection and AuditingDbCommand, and threads
the id through NotifyHelper/NotifyTarget. The S&F retry-loop cached rows
(CachedCallLifecycleBridge) are out of scope here.

tests/ScadaLink.SiteRuntime.Tests/Scripts/DatabaseCachedWriteEmissionTests.cs

@@ -39,6 +39,12 @@ public class DatabaseCachedWriteEmissionTests
     private const string InstanceName = "Plant.Pump42";
     private const string SourceScript = "ScriptActor:WriteAudit";
 
+    /// <summary>
+    /// Audit Log #23: a fixed per-execution id so the cached-row tests can
+    /// assert <see cref="AuditEvent.ExecutionId"/> against a known value.
+    /// </summary>
+    private static readonly Guid TestExecutionId = Guid.NewGuid();
+
     private static ScriptRuntimeContext.DatabaseHelper CreateHelper(
         IDatabaseGateway gateway,
         ICachedCallTelemetryForwarder? forwarder)
@@ -47,9 +53,10 @@ public class DatabaseCachedWriteEmissionTests
             gateway,
             InstanceName,
             NullLogger.Instance,
-            // Audit Log #23: execution-wide correlation id. Cached rows keep
-            // CorrelationId = TrackedOperationId, so any value works here.
-            Guid.NewGuid(),
+            // Audit Log #23: the per-execution id stamped into ExecutionId on
+            // every script-side row. Cached rows keep CorrelationId =
+            // TrackedOperationId (the per-operation lifecycle id).
+            TestExecutionId,
             siteId: SiteId,
             sourceScript: SourceScript,
             cachedForwarder: forwarder);
@@ -79,7 +86,10 @@ public class DatabaseCachedWriteEmissionTests
         Assert.Equal(AuditKind.CachedSubmit, packet.Audit.Kind);
         Assert.Equal(AuditStatus.Submitted, packet.Audit.Status);
         Assert.Equal("myDb", packet.Audit.Target);
+        // CorrelationId is the per-operation lifecycle id (TrackedOperationId);
+        // ExecutionId is the per-execution id from the runtime context.
         Assert.Equal(trackedId.Value, packet.Audit.CorrelationId);
+        Assert.Equal(TestExecutionId, packet.Audit.ExecutionId);
 
         Assert.Equal(trackedId, packet.Operational.TrackedOperationId);
         Assert.Equal("DbOutbound", packet.Operational.Channel);